This invention relates to a differential amplification circuit, and more particularly to the differential amplification circuit able to generate an output having a controlled in-phase component.
It is often required that the DC level of the output of a differential amplification circuit designed to output a voltage be precisely controlled. To meet this requirement, the difference between the in-phase component of the output voltage and a reference value is negatively fed back to the circuit.
More specifically, a differential signal input to the input terminals of the differential amplification circuit is amplified by a differential amplifier making a part of the circuit, and is output from the output terminals of the circuit. The in-phase component of the amplified signal is detected at the output terminals of the circuit. The in-phase component is input to the inverting input terminal of an operational amplifier. The reference value is input to the noninverting input terminal of the operational amplifier. Hence, the operational amplifier outputs the difference between the in-phase component and the reference value. This difference is negatively fed back to the differential amplifier, thereby controlling the DC level of the output voltage.
The operational amplifier must be a large-scale one, however. The amplification circuit is inevitably large and can hardly be made in the form of an integrated circuit.